Hazard Assessment of Urban Trees along the Bagmati River Corridor: A Case Study from Kathmandu Metropolitan City, Ward Number 8

Urban trees are extremely significant and provide numerous advantages for both the environment and people. In order to provide a healthy and sustainable environment, green spaces have long been seen as a crucial component of contemporary cities. Nevertheless, as urbanization and population growth have accelerated, environmental challenges have become a major worldwide issue. This study mainly focuses on the assessment of hazardous trees along the Bagmati river corridor and documents major tree species for urban forestry. The study was conducted in ward number 08 of Kathmandu metropolitan city. Total enumeration was carried out by recording information on trees through direct observation of the whole site. The International Society of Arboriculture (ISA) tree hazard evaluation method was used as a tree risk assessment tool. A total of 74 trees were recorded from the study site. Grevillea robusta, Cinnamomum camphora, Ficus bengalensis, F. religiosa, and so on were the major species planted along the Bagmati corridor. The trees were categorized in varying degrees of hazard. Forty-seven trees were less hazardous, 24 were semihazardous, and 3 were hazardous with hazard rates of 2.91, 6.04, and 9, respectively. Jasminum nudiflorum was the only hazardous species recorded followed by semihazardous species such as Morus alba and F. religiosa among other species, and Eucalyptus camaldulensis, Citrus limon, Psidium guajava, Alnus nepalensis, and so on were least hazardous tree species. The hazardous tree in urban areas increases the risk to people and public as well as private properties. There is a need for the removal of such hazardous trees and planting the right species at the right time. Moreover, regular inspection and a clear policy for urban trees are needed.


Introduction
Te term "urban forestry" was frst used in 1965 by [1] as part of a study on the successes and failures of a municipal tree planting program.Urban forestry is a concept that originated in North America in response to the growing importance of tree-dominated areas as well as human pressure on green spaces [2].Urban forestry is the practice of forestry that is defned as the management of publicly and privately held lands in and near metropolitan centers.It includes parks, gardens, roadside plantation, stream bank plantation, and plantation in private property and forest near urban areas [3].Urban forests contribute in sustainable development of cities through improving quality of life and environmental qualities [4].In this type of forestry, trees are grown primarily for ornamental and fowering trees and shrubs, not for the production of fuel, food, or timber, to serve as recreation forests for urban inhabitants [5].
Urban parks are seen as signifcant drivers of the sustainable development of cities in both developed and developing nations.Tey provide a wide range of advantages to locals and visitors, including recreational activities, fresh air, aesthetically appealing features, and ecological purposes [6].Urban green and blue areas that are easily accessible and of the highest quality enhance the local population's health signifcantly (European Environment Agency [7]).Green spaces increase biodiversity, reduce noise levels, and improve air quality [8,9].Urban and periurban forestry (UPF) has become a signifcant concern for policymakers and planners because of increasing urbanization [3].Urbanization, which is the term for the movement of people from rural to urban regions, began in the Kathmandu valley in the late 1950s, but since 1970, the increase has been unmanaged [10].In Nepal, the practice of urban forestry dates back to the Malla reign by King Jayasthiti Malla (1380-1395 AD) issuing an order to his ofcials and commoners to plant trees alongside walking streets and wells [11].
A typical 22% and 17%, respectively, of the total municipal area in Hill and Terai are covered by forests.In a mountainous area, it encompasses 30% of the entire municipal territory.Te coverage in the Kathmandu valley is 3% [12].In Kathmandu, the Department of Road (DOR) has been appointed to plant trees along the sides of the roads, while DOF is the organization with the necessary expertise in tree management and silviculture [13].Integrative, strategic, multipurpose, transdisciplinary, and social inclusivity are among the concepts of urban forestry [14].In recent years, the government has emphasized urban forestry through its various programs, including "Nepal Clean Environment Grand Expedition 2075 AD" and the Forest Decade Program (2014-2023) [3].
Despite the importance, environmental assets in general are frequently the ones that are most neglected.Tis is because the majority of poor nations often lack a scientifc grasp of how urban trees, parks, and gardens beneft people [6].Also, as urban areas increase, importance of benefts of urban forest as well as challenges to their conservation and maintenance will increase [15].Urban trees are more likely to be sitestressed due to a number of factors.Most urban trees survive on construction-altered soils that may be compacted, poorly drained, high in clay, sand, or gravel, very alkaline, or littered with construction debris [16].
Despite various urban forestry programme conducted by DoF in Nepal, they still possess threats to people and properties commonly known as hazard.Hazards are things, conditions, or situations that have the potential to cause harm [17].Tree hazards could be because of defects in trees, dead or dying trees, dead branches from living trees, or living trees that are unstable owing to structural faws or other causes that are close to people or other property (a target) and might result in property damage, human harm, or even death in the case of failure [18,19].A tree defect is defned as a fault, faw, or abnormality of the normal tree structure and function resulting in inadequate performance or failure [20].Defects could be seen in the crown, branch, trunk, and roots.
Due to the usage of land for business and habitation uses, Kathmandu, the capital and most populated city of Nepal, lacks green parks and trees.As of 2017, just 3% of Kathmandu was covered with forest, according to the National Urban Development Strategy released by MoUD [12].In addition, the shift of multiple land uses within the city as well as the neighboring urban fringes, together with industrialization in these regions, caused the decline of existing tree cover [11].
Tus, this study has been conducted to identify the planted tree species along the Bagmati river corridor and the defects in the tree species and hazards caused by them.Tis study also helps environmental managers and planners to understand and take into account the less tangible values that people derive from contact with nature.[21,22].

Materials and Methods
Te map of the study area is shown in Figure 1.

Sampling Method.
Total enumeration of trees of the whole study site was done through direct observation.Information about trees (name of species, coordinates, girth of the tree, height of the tree, and defects) was recorded through direct observation of the site.Te girth was measured using a diameter tape (cm) at diameter at breast height and height using a rangefnder (m).

Hazard Assessment.
Guidelines from the book "A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas" [23] was used to identify the hazardous tree.Te steps given in the book are as follows: (i) Identifcation of trees (ii) Formulation of evaluation parameters (iii) Identifcation of the tree's structural defects and afected structural components likely to fail (iv) Summarization of defects and the rank likelihood of structural failure (v) Identifcation of the target in danger (vi) Summarization of hazard rating Taking the average index, the sample site was classifed as hazardous, semihazardous, and less hazardous.
Ms-Excel and ArcGIS were used to analyze data.Data were presented in the form of tables, charts, and diagrams.Te International Society of Arboriculture (ISA) tree hazard evaluation method [23] was used.Hazard rating which is a summation of three components is shown as follows: 2 Scientifca failure potential + size of defective part + target rating � hazard rating. ( Each component has a four-point rating system, for a combined total of twelve points, which is the maximum hazard rating.Components are as follows: (A) Failure Potential.Te potential of a tree or tree part to fall before another inspection is called failure potential.On basis of the presence of a type of defect, trees are classifed as low failure potential to high failure potential and the value is assigned from 1 to 4, respectively: (1) Low.  1 shows the hazard rating scores for categorization of trees and sites.

Major Tree Species Listed in the Study
Area.In the study site, we recorded 74 total trees of 22 diferent species that occurred in the sample site.Grevillea robusta was seen maximum followed by Cinnamomum camphora, whereas only one number of species such as Phyllanthus emblica, Abies procera, and Morus alba were recorded.Table 2 shows the species types recorded throughout the site.Also, saplings of Prunus cerasoides, Ficus elastica, Mangifera indica, Eucalyptus camaldulensis, Ficus bengalensis, and Cinnamomum camphora planted along the corridor were seen.
Te results align with the fndings of a study conducted by in Pakistan and Gautam et al. [24] in Kathmandu, which reported that Grevillea robusta was the most commonly planted tree species in urban areas, followed by Cinnamomum camphora, Ficus spp., Eucalyptus camaldulensis, and so on.Te major purpose of this urban plantation seems for ornamentation as well as to maintain the urban ecosystem intact.Besides, road site trees ultimately fulflled the amenity, shelter, wind frm, and evergreen and urban park [25].Tis fnding is also supported by a study by Knaus et al. [26] which found that certain tree species such as Calliandra hematocephala and Juniperus chinensis are more commonly planted in urban areas due to their aesthetic value.

Girth Distribution of Species.
In the study site, it was found that the highest girth was of Peepal (Ficus religiosa), i.e., 233.8 cm followed by Eucalyptus camaldulensis, i. e., 181 cm, both Kangiyo (Grevillea robusta) and Kimbu (Morus alba) with similar girth, i.e., 120.5 cm and so on, while the lowest girth was of Amba (Psidium guajava), i.e., 9cm followed by Nibuwa (Citrus limon) of 14 cm and Kauli phool (Pileostegia viburnoides) of 17 cm and so on, as shown in Figure 2.

Height Distribution of Species.
In the study site, Eucalyptus camaldulensis had an average height of 23 m, recorded as the highest, followed by Ficus religiosa 10.83 m and Elaeocarpus sphaericus 9 m and the lowest was of Nibuwa (Citrus limon), i.e., 1 m followed by Khari (Celtis australis), Jaiful (Jasminum nudiforum), Bottlebrush (Calliandra hematocephala), and Amba (Psidium guajava), all four species having average height of 2 m as shown in Figure 3.

Tree Hazard
Rating with respect to the Species.A hazard rating was given for each tree of each species, and average hazard rating was calculated for each species.Using this hazard rating of trees, species were classifed as less hazardous, semihazardous, and hazardous trees.
Out of the total 23 tree species recorded, Jaiful (Jasminum nudiforum) was the only hazardous species with 9 as hazard rating, whereas Amba (Psidium guajava), Eucalyptus camaldulensis, Nibuwa (Citrus Limon), and Uttis (Alnus nepalensis) had less hazard rating (1) which can be seen in Figure 4. Te average hazard rating for less hazardous, semihazardous, and hazardous species was obtained as 2.38, 5.38, and 9, respectively.

Tree Hazard Rating with respect to the Hazardous Tree.
A hazard rating was given for each tree.Using this hazard rating of trees, trees were classifed as less hazardous, hazardous, and semihazardous.
Our study showed a variety of possible tree hazards along the Bagmati river corridor, including structural defects, root damage, and pests and diseases.Te majority of the trees surveyed had some degree of decay or rot, increasing the likelihood of failure during severe wind or storm occurrences.Furthermore, several trees were shown to have weakened root systems as a result of soil compaction or erosion, which might increase their risk of failure.
Results shown by [24] identifed a range of tree species in the area, many of which were hazardous and needed to be removed immediately for public safety.
Moreover, our fndings are consistent with several studies that have identifed defects (knots, splits, hollowness, and so on) as common tree hazards in urban areas.A study by Ding et al. [27] in some major parks of Hongkong found that nearly half of the urban trees had shown some degree of defect While another study by Liu et al. [28] found that stem and root damage was the most common cause of tree failure in an urban park in Hong Kong.
Te distribution of trees based on hazard rating is shown in Figures 6-8, which shows the distribution of hazardous, semihazardous, and less hazardous trees, respectively.

. Discussion
Our study found a signifcant number of trees with structural defects and symptoms of decay, posing a serious risk to public safety and property.Te fnding is consistent with the 4 Scientifca fndings of many urban studies.For example, Leers et al. [29] conducted a comprehensive analysis of urban trees in Melbourne, Australia, and examined six indicators of urban tree establishment, emphasizing the importance of frequent tree inspections and maintenance for addressing structural defects.
Te weakened root systems of many trees along the Bagmati river corridor, which are frequently caused by soil compaction and erosion, resonate with concerns raised in studies such as Wattenhofer and Johnson's [30] study on the efects of young urban tree death on future success and urban development on tree root health.Tey discovered that soil compaction can limit root growth and water infltration, making trees more susceptible to windthrow and uprooting.
Our risk assessment approach, which takes into account both the likelihood as well as consequences of tree failure, is consistent with best practices in urban tree management [31].Prioritizing trees near high-trafc areas, buildings, and infrastructure for management is consistent with recommendations of Pokorny et al. [16], in their study on urban tree risk   336500 .000000337000 .000000337500 .000000338500 .000000338000 .000000339000 .000000336500 .000000337000 .000000337500 .000000338500 .000000338000 .000000339000 .0000000 0.  8 Scientifca management.Tis particular strategy can more efciently allocate resources to mitigating the most signifcant risks and hazards.It is important for the Kathmandu district's relevant authorities to monitor and address these issues in order to sustain healthy trees in urban areas.

Conclusion
A total of 74 trees of 23 diferent species were recorded along the Bagmati river corridor of KMC ward number 8. Major plant species along the Bagmati river corridor were Indian Gooseberry, Chinaberry tree, Banyan, Red Powderpuf, Eucalyptus, Prunus, and Mangifera were also seen along the river corridor.Jasminum was the only hazardous tree followed by other semihazardous species Morus, F. religiosa, and so on, among other tree species, and Eucalyptus, Citrus, P. guajava, and Alnus were least hazardous tree species.Also, 3 hazardous trees, 24 semihazardous trees, and 47 less hazardous trees were present in the area with hazard index 9, 6.04, and 2.91, respectively, necessitating the immediate attention of the relevant authorities.It was found that the 336500 .000000337000 .000000337500 .000000338500 .000000338000 .000000339000 .000000336500 .000000337000 .000000337500 .000000338500 .000000338000 .000000339000 .000000 Less hazardous trees River KMC Ward8 3064400 .0000003065100 .0000003065800 .0000003066500 .0000003067200 .0000003067900 .0000003064400 .0000003065100 .0000003065800 .0000003066500 .0000003067200 .000000Scientifca existing management is inadequate and that hazardous trees need to be removed.It is further recommended to focus on tree management and species selection promoting research on location variables and their efects on species and their silvicultural characteristics, as well as their social and economic values.Also, ornamental species such as Eucalyptus and Juniperus and fowering species such as Grevillea, Calliandra, and Jacaranda are encouraged to be planted along the 2 * 2 m spacing in an orderly manner.It is also essential for the Kathmandu district authorities to implement regular tree inspections, soil management practices, and defects and pest/diseases monitoring to safeguard public safety and maintain a healthy urban forest.

Figure 4 :
Figure 4: Hazard rating with respect to tree species.
Juniper, Noble Fir, Winter Jasmine, Black Plum, Silk oak, Camphor tree, Honeyberry, Mulberry, Cottonwood Poplar, Sacred Fig, Stone fruit, and so on.Saplings of plants such as

Figure 8 :
Figure 8: Distribution map showing less hazardous trees.
Te annual temperature of the district varies from 19 °C to 30 °C during autumn and from 2 °C to 17 °C during winter, whereas the climate varies from subtropical to temperate.Te annual precipitation is about 1,400 mm which falls mostly from May to September, with 80% during monsoon

Table 1 :
Hazard rating scores for categorization of trees and sites.

Table 2 :
List of species recorded in the study area.
Figure 6: Distribution map showing hazardous trees.